A prior art apparatus for grasping and rotating a disk for treating its both surfaces, has a pair of grasp means for grasping a central portion of the disk from both sides for indexing and rotating it. Such an apparatus is disclosed in Japanese Patent Ko-kai (Laid-Open) Publication No. 61-71961.
There is another kind of disk grasping and rotating apparatus which has a pair of grasp means for grasping a disk from both sides to index the disk. A rotatable chuck extends from one of the grasp means into a central opening of the disk, and a rod which is slidably received in the chuck spreads the chuck so as to support the disk from the inside. Next, the grasp means separate from the disk and the disk is rotated by rotating the chuck which grasps the disk. This apparatus is disclosed in Japanese Patent Ko-kai (Laid-Open) Publication No. 61-219562.
In order to simultaneously treat both sides of a disk by using treating tapes, the disk must be indexed at a center between a pair of rolls such that the treating tapes can be pushed on its surfaces.
The aforementioned disk grasping and rotating apparatus can accurately grasp and rotate a disk, but it needs pair of grasp means in order to position or index the disk.
The apparatus which support a disk from the inside and rotates it by means of a chuck means also must be able to position or index the disk by means of a pair of grasp means.